Fuel cells are well known and are commonly used to produce electrical power from hydrogen containing reducing fluid fuel and oxygen containing oxidant reactant streams to power electrical apparatus such as generators and transportation vehicles. In fuel cells of the prior art, it is known to utilize a proton exchange membrane (“PEM”) as the electrolyte. As is well known, protons formed at an anode catalyst layer move through the electrolyte to a cathode catalyst layer while electrons move through a circuit to power a load. Fuel cell product water is formed at the cathode catalyst as the electrons complete the circuit back to the fuel cell and as an oxidant passes adjacent the cathode catalyst.
Use of such fuel cells to power transportation vehicles necessarily involves many start-stop cycles, some of which will occur in sub-freezing ambient conditions. Typically, fuel cell product water in a PEM fuel cell is at least partially recycled or utilized to hydrate membranes, to humidify reactant streams, to remove heat from a membrane electrode assembly (“MEA”), to support fuel reformers, and for other well-known purposes. In sub-freezing ambient conditions, freezing of fuel cell water may block flow paths that direct reactant streams through the fuel cell, thereby disrupting fuel cell performance.
Efforts to minimize problems of freezing of fuel cell product water include use of complicated and costly fuel fired heaters, electrical heaters using parasitic power from a fuel cell power plant battery, complex antifreeze solutions within coolant water flow streams, etc. It is also known to rely exclusively upon heat generated by an operating fuel cell upon start-up of the fuel cell to prevent fuel cell product water from freezing and blocking reactant stream flow channels. Such a start-up is frequently referred to as a “boot strap start-up”, because the fuel cell itself provides its own heat for preventing freezing of fuel cell product water produced during the start-up.
Unfortunately, however, when ambient conditions are extremely cold, or when a fuel cell is only operated for a short duration in sub-freezing ambient conditions (such as a two-three minute or shorter operation of a vehicle), fuel cell product water generated upon start-up may remain at sub-freezing conditions within pores of the cathode catalyst layer and within reactant flow pores or channels adjacent the cathode and/or anode catalyst layer. Such sub-freezing fuel cell water may then freeze and block or limit access of gaseous reactant streams to fuel cell catalysts. This is an especially troublesome problem if a fuel cell powered vehicle experiences one or more aborted starts, which means an operator initiates a fuel cell shut down, typically by turning off a fuel cell on/off switching device during a fuel cell start-up process prior to the fuel cell achieving a freeze-safe operating temperature. This may occur for a variety of reasons typical of normal vehicle operating circumstances, such as an operator returning into a residence to get a forgotten item, very short trips, such as to a neighbor's residence, etc. The frozen fuel cell water may then substantially impede subsequent efforts at starting up the fuel cell in the sub-freezing ambient conditions by prohibiting and/or severely restricting flow of reactant streams adjacent the fuel cell catalysts, especially adjacent a cathode catalyst. The key point or main problem is that a power plant shut down signal is sent to the power plant controller when the power plant is in no condition to shut down due to its operating environment.